A multiphase expansion foam fire extinguishing agent based on excess sludge and its preparation method

Abstract

This invention discloses a multiphase expandable foam fire extinguishing agent based on residual sludge and its preparation method. The fire extinguishing agent comprises separately packaged gas and liquid-solid phases. The gas phase is a driving gas, and the liquid-solid phase is a mixture of foam protein and EPS-ALE flame-retardant particles at a mass ratio of 1:0.12-0.20. The EPS-ALE flame-retardant particles are nano-silica particles coated with extracellular polymers and alginate-like substances. This invention coats the silica surface with extracellular polymers and alginate-like substances. The alginate-like substances not only fix the extracellular polymers more extensively and stably on the nano-silica surface, but also synergistically enhance the flame retardancy of the extracellular polymers, resulting in a synergistic flame-retardant effect and improving the stability and fire resistance of the foam fire extinguishing agent. Furthermore, the extracellular polymers, alginate-like substances, and proteins of this invention are all extracted from residual sludge, achieving harmless treatment of the sludge and reducing production costs, thus showing great application potential.

Description

Technical Field

[0001] This invention relates to a multiphase intumescent foam fire extinguishing agent, specifically to a multiphase intumescent foam fire extinguishing agent based on residual sludge biomass recycling technology and its preparation method, belonging to the field of fire extinguishing agent technology. Background Technology

[0002] With the progress of research and the advancement of technology, wastewater treatment plants have been able to meet the requirements for removing pollutants from water. However, how to reduce and render harmless the large amount of excess sludge generated by wastewater treatment plants and then recycle it as a resource will be the focus of future research.

[0003] Currently, waste sludge, as a type of solid waste, is mainly treated through sanitary landfill. Even when extracting components from waste sludge, most studies focus on the recovery of single biological materials, neglecting research on the continuous recovery of multiple biological materials. This results in a significant waste of resources as much biomass is discarded as waste. Waste sludge contains a large amount of organic matter, up to 70% of its dry weight, including various biological materials. Protein has the highest content, accounting for 30%–60% of the sludge's dry weight, and can be used as a raw material for foam fire extinguishing agents. Extracellular polymers (EPS) are composed of proteins (structural proteins and enzymes), polysaccharides, nucleic acids and lipids, humic substances, and some intercellular polymers, accounting for approximately 40% of the sludge biomass. Alginate (ALE) is mainly composed of guluronic acid (G) and mannuronic acid (M), exhibiting hydrogel properties similar to alginate. When combined with calcium ions, it forms an "egg-box" structure, i.e., a gel. These biomass materials recovered from sludge have broad application prospects in the field of foam fire extinguishing agent preparation.

[0004] Extracellular polymers can combine with coke, inorganic matter, and carbon residues formed during combustion, further expanding and foaming to form a porous foam carbon layer that prevents heat transfer, reduces the release of combustible gases, and isolates oxygen. The phosphate groups in the phosphoproteins contained in the extracellular polymers can release phosphorus-oxygen free radicals (PO·) when decomposed by heat. These free radicals can capture H· and ·OH in the gas phase that promote combustion reactions, blocking or slowing down hydrocarbon branching or combustion chain reactions. The water vapor and carbon dioxide generated by the reaction can reduce the surface temperature and dilute the concentration of combustibles in the gas phase. The nitrogenous bases in DNA can release ammonia, which can dilute the oxygen concentration in the gas phase, thereby achieving flame suppression. Therefore, it can be added to foam fire extinguishing agents as an anti-burning agent.

[0005] Alginate also has a flame-retardant effect. During combustion, it can form a sticky residue mainly composed of carbonized substances, blocking heat transfer. Similar to extracellular polymers, alginate also produces a large number of heat-absorbing groups when it is heated and decomposes, reducing the surface temperature of the fabric. The water vapor and carbon dioxide generated by the reaction can also dilute the concentration of gaseous combustibles. The hydrogel formed by alginate and calcium ions is very easy to stick together when heated and decomposes, which increases the heat transfer resistance. The added calcium ions will generate CaCO3 and Ca(OH)2 when burning, forming a protective layer that prevents combustible gases from being released to the outside and prevents external oxygen from diffusing inward. Summary of the Invention

[0006] In response to the current situation of residual sludge, this invention provides an effective method for its resource recovery, namely, the comprehensive extraction of biomass from the residual sludge for use in the preparation of fire extinguishing agents. This invention provides a multiphase intumescent foam fire extinguishing agent based on residual sludge. This foam fire extinguishing agent uses residual sludge as a raw material, and foam proteins, extracellular polymers, and alginates extracted from the residual sludge are used in the preparation of the fire extinguishing agent, which has the advantages of low production cost and good fire extinguishing effect.

[0007] The "expandable" in the intumescent foam fire extinguishing agent of this invention refers to the fact that when the fire extinguishing agent is used, the phosphorus-containing groups in the extracellular polymeric material combine with other inorganic substances (such as calcium ions) during combustion to form a thermally stable inert substance. This inert substance combines with the coke produced by the combustion of other organic substances (such as cellulose, polysaccharides, etc.) in the extracellular polymeric material, further expanding and foaming to form a dense, highly thermally stable foam-like char layer covering the surface of the combustible material, preventing heat transfer, reducing the release of combustible gases, and isolating oxygen.

[0008] A multiphase intumescent foam fire extinguishing agent based on residual sludge comprises separately packaged gas and liquid-solid phases, wherein the gas phase is a driving gas, and the liquid-solid phase is a mixture of foam protein and EPS-ALE flame-retardant particles at a mass ratio of 1:0.12-0.20; the preparation method of the EPS-ALE flame-retardant particles is as follows:

[0009] (1) Take the remaining sludge, centrifuge it, and collect the wet sludge at the bottom;

[0010] (2) Disperse the wet sludge with water, then add Na2CO3 solution to adjust the pH to 10.5-11.5, then heat it with stirring, centrifuge it after treatment, filter the supernatant to obtain an extracellular polymer solution;

[0011] (3) Using the extracellular polymer solution from step (2) as raw material, place it in a 3500 Da dialysis bag for dialysis. Adjust the pH of the obtained dialysis extract to 2.15-2.25 with acid while stirring. Then centrifuge the dialysis extract after pH adjustment, collect the gel-like particles at the bottom, and add Na2CO3 solution to the gel-like particles while stirring until the pH reaches 8.3-8.7 to obtain an alginate solution.

[0012] (4) The alginate solution was freeze-dried under vacuum to obtain dry alginate, and then it was prepared into a 2-4 wt% alginate compound solution with Na2CO3 solution at pH 8.3-8.7.

[0013] (5) Soak the nano-silica in the alginate compound solution, then add CaCl2 solution to the alginate compound solution under stirring until gel particles are produced, then freeze dry under vacuum, collect the gel particles, and obtain nano-silica coated with alginate.

[0014] (6) Mix the extracellular polymer solution, dicyandiamine and water from step (2) to obtain a flame retardant solution. Place the nano-silica coated with alginate into the flame retardant solution and heat it under stirring. Then take out the resulting gel particles and freeze-dry them under vacuum to obtain EPS-ALE flame retardant particles.

[0015] Furthermore, the present invention extracts an extracellular polymer solution and an alginate solution from the remaining sludge through steps (1)-(3). The extracellular polymer solution contains alginate, and therefore the extracellular polymer solution is used as a raw material to further extract the alginate solution. Since both the extracellular polymer solution and the alginate solution are raw materials required by the present invention, in actual operation, the extracellular polymer solution can be prepared in large quantities at once, and then the alginate solution can be further prepared using it as a raw material. Alternatively, the extracellular polymer solution can be prepared first, and then the alginate solution can be prepared according to steps (1)-(3).

[0016] Furthermore, in step (2), the mass ratio of wet sludge to water is 1:15-20, and the concentration of Na2CO3 solution is 0.5-1.5mol / L.

[0017] Furthermore, in step (2), the wet sludge dispersion is heated at 75-85℃ for 30-40 minutes with stirring. The stirring speed is generally 350-450 r / min.

[0018] Furthermore, in step (3), the extracellular polymeric solution is placed in a 3500 Da dialysis bag and dialyzed for 24-26 hours, during which the water used for dialysis is changed every 12-13 hours.

[0019] Further, in step (3), the extract is dialyzed at room temperature with slow stirring at 80-120 rpm, and then acid is added to adjust the pH to 2.15-2.25 to obtain gel-like particles, which are acidic alginate (ALE). The acid used can be any commonly used inorganic acid, such as hydrochloric acid with a concentration of 1-2 mol / L.

[0020] Furthermore, in step (3), the concentration of the Na2CO3 solution is preferably 0.05-0.15 mol / L.

[0021] Furthermore, in step (4), in order to reduce the damage to the alginate structure, it is vacuum freeze-dried (freeze-drying is the same as lyophilization) before compounding. Vacuum freeze-drying is preferably carried out at a temperature of -65 to -75°C, such as -65°C, -72°C, or -75°C, and the processing time is generally 70-75 hours.

[0022] Furthermore, in step (5), the particle size of the nano-silica is 70-400nm, for example 70nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm.

[0023] Furthermore, in step (5), the nano-silica is immersed in an excess of alginate solution for 22-26 hours to ensure sufficient contact between the alginate and the nano-silica. After immersion, CaCl2 solution is added to the solution to allow the alginate and calcium chloride to react and form a gel layer on the surface of the nano-silica. The nano-silica particles coated with the gel layer become significantly larger, resulting in gel particles. The concentration of the CaCl2 solution used is 0.05-0.15 mol / L, and the CaCl2 solution is added while stirring until gel particles are formed.

[0024] Furthermore, in step (5), it is preferable to add CaCl2 solution to the alginate compound solution under stirring. The stirring speed can be 50-100 r / min, for example, 50 r / min, 60 r / min, 80 r / min, or 100 r / min.

[0025] Furthermore, in step (5), in order to reduce the damage to the alginate structure, the gel particles are vacuum freeze-dried. Vacuum freeze-drying is preferably carried out at a temperature of -65 to -75°C, such as -65°C, -72°C, or -75°C, and the processing time is generally 70-75 hours.

[0026] Furthermore, in step (6), the content of extracellular polymeric solution in the flame retardant solution is 18-25wt%, for example 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, and the content of dicyandiamide is 3-8wt%, for example 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%.

[0027] Furthermore, in step (6), in order to protect the integrity of the gel particles, nano-silica coated with alginate is added, and then the mixture is slowly stirred at 50-60 r / min for heating treatment. The heating treatment temperature is 38-45℃, and the heating treatment time is 20-30 min, in order to promote better bonding between the flame retardant solution and the gel particles.

[0028] Further, in step (6), after heat treatment, gel particles with extracellular polymers coated on the surface of nano-silica coated with alginate are obtained. The gel particles are then removed and freeze-dried under vacuum to obtain EPS-ALE flame-retardant particles. Vacuum freeze-drying is preferably carried out at a temperature of -65 to -75°C, for example, -65°C, -72°C, or -75°C, and the processing time is generally 70-75 hours.

[0029] Furthermore, the foam protein used in this invention is a foam protein stock solution recovered from residual sludge. The resulting foam protein stock solution also has a fire extinguishing effect and is low in cost.

[0030] Furthermore, in a specific embodiment of the present invention, the foam protein stock solution is obtained by method A as follows:

[0031] (A1) Take the remaining sludge, centrifuge it, and collect the wet sludge at the bottom;

[0032] (A2) Using wet sludge or the sludge precipitate remaining after extracting extracellular polymers in step (2) above as raw material, the raw material is dispersed in water, and then the pH is adjusted to 11-13 with NaOH solution. Then, it is stirred and heated at 115-125℃ for 3-5 hours, then cooled and centrifuged. The supernatant obtained is dialyzed and dried to obtain protein powder. The protein powder is prepared into a solution with a concentration of 2-4wt% with phosphate solution, which is the foam protein stock solution.

[0033] Furthermore, in step A2, the mass ratio of wet sludge or residual sludge sediment to water is 1:15-20.

[0034] Furthermore, in step A2, the concentration of the NaOH solution is 1-2 mol / L.

[0035] Furthermore, in step A2, the stirring speed is 80-120 r / min.

[0036] Furthermore, in step A2, the pH of the phosphate solution is 7.

[0037] Furthermore, in a specific embodiment of the present invention, the foam protein is obtained in accordance with the method described in CN114768162B, and the specific steps are as follows:

[0038] (B1) The sludge remaining after extracting the extracellular polymer in step (2) above is precipitated as raw material, and the raw material is dispersed in water to obtain sludge suspension;

[0039] (B2) Add the sludge suspension to a container and first sonicate it in a cold water bath at 0-5℃ for 5-15 minutes. The ultrasonic power is 35-45kHz, and the ultrasonic intensity is 0.2-0.4W / mL of sludge suspension. Then, while sonicating, introduce ozone into the sludge suspension in the form of micro-aeration. The ozone bubbles in the sludge suspension should be less than or equal to 50μm, and the ozone concentration should be 8-10mg O. 3 / L, ozone flow rate is 0.3-0.6L / min, ozone introduction time is 5-10min;

[0040] (B3) The sludge suspension after ozone treatment is centrifuged, and the resulting precipitate is added to a sodium hydroxide solution with a pH of 11-13 for protein extraction.

[0041] (B4) Centrifuge the mixture from step (B3) to obtain the supernatant, dry the supernatant to obtain protein powder, and prepare a 2-4 wt% solution of the protein powder with phosphate solution, which is the foam protein stock solution.

[0042] Furthermore, in step B3, the volume ratio of the precipitate obtained by centrifugation to the NaOH solution is 1:5-15.

[0043] Furthermore, in step B3, protein extraction is carried out under stirring at a temperature of 40-45℃ for 15-20 minutes.

[0044] Furthermore, in step B4, the pH of the phosphate solution is 7.

[0045] Furthermore, in the above-mentioned preparation methods of EPS-ALE flame retardant particles and foam protein stock solution, the centrifugation conditions involved are: temperature 3-4℃, rotation speed 4000-41000r / min.

[0046] Furthermore, the driving gas is at least one of nitrogen, argon, and heptafluoropropane. Preferably, the driving gas is a mixture of nitrogen, argon, and heptafluoropropane. More preferably, the molar ratio of nitrogen, argon, and heptafluoropropane is 45:40:15.

[0047] This invention also provides a method for preparing the above-mentioned multiphase expandable foam fire extinguishing agent based on residual sludge, comprising the following steps:

[0048] (1) Mix foam protein and EPS-ALE flame retardant granules at a mass ratio of 1:0.12-0.20, stir evenly, and then pack into cans for later use;

[0049] (2) Pack the driving gas into a can for later use.

[0050] The present invention has the following beneficial effects:

[0051] 1. This invention first coats nano-silica with an alginate hydrogel, and then coats it with an extracellular polymer flame retardant. Research revealed that nano-silica is an inorganic phase, while the extracellular polymer is an organic phase. Experiments showed that if nano-silica is directly immersed in the extracellular polymer solution for coating, the amount of extracellular polymer coating on the silica surface is small and very unstable, easily detaching. Therefore, utilizing the hydrogel properties of alginate, nano-silica particles are first coated with an alginate hydrogel, and then a special process is used to coat the organic-phase extracellular polymer flame retardant solution onto the equally organic-phase alginate hydrogel. This not only solves the problem of poor adhesion between the extracellular polymer flame retardant solution and nano-silica particles, resulting in more and more stable extracellular polymer coating, but also, since both the alginate hydrogel and the extracellular polymer have flame retardant effects, they can produce a synergistic flame retardant effect, further enhancing the fire extinguishing agent's anti-burn performance and foam stability, leading to better fire extinguishing results.

[0052] 2. The solid phase of the fire extinguishing agent of this invention is EPS-ALE flame-retardant particles with a multi-layered structure. These flame-retardant particles contain an alginate hydrogel layer and an extracellular polymer layer. On the one hand, the extracellular polymer, as an anti-burning agent, is added to the foam fire extinguishing agent and combines with the coke, inorganic matter, and carbon residue formed during combustion. It further expands and foams to form a porous foam carbon layer to prevent heat transfer, reduce the release of flammable gases, and isolate oxygen, thereby enhancing the anti-burning performance of the foam fire extinguishing agent. On the other hand, the nano-silica exposed after the extracellular polymer decomposes under heat can fill the gaps between the foams, forming a more tightly bonded skeletal structure between the foams, thus enhancing the foam stability. Furthermore, utilizing the hydrogel properties of alginate, an organic coating layer is first applied to the nano-silica, followed by the application of the extracellular polymer. This solves the problem of poor bonding between the organic phase (extracellular polymer) and the inorganic phase (nano-silica), making the extracellular polymer more firmly coated on the silica surface. The flame-retardant particles used in this invention overcome the shortcomings of traditional foam extinguishing agents, such as easy foam breakage and poor fire resistance, and enhance the stability and fire resistance of foam extinguishing agents.

[0053] 3. The alginate of the present invention can not only fix more and more stable extracellular polymers on the surface of nano-silica, but also has a synergistic effect with extracellular polymers in terms of flame retardancy, thus achieving a synergistic flame retardant effect.

[0054] 4. This invention extracts extracellular polymers, alginates, and proteins from residual sludge. The recovered foam protein is used as the liquid phase of the fire extinguishing agent. The extracellular polymers and alginates are used to coat the nano-silica in the fire extinguishing agent, which has the advantages of low production cost and good fire extinguishing effect, and can be applied in the field of fire fighting. This invention fully enhances the application value of sludge by continuously and fully extracting the biomass, which reduces the amount of waste generated and facilitates subsequent treatment, while further exploring the recycling potential of raw materials and making the most of resources.

[0055] 5. The main raw materials of the foam fire extinguishing agent of this invention are biomass extracts and nano-silica, so it has excellent biodegradability, is very environmentally friendly, green and environmentally friendly, and overcomes the environmental risks of traditional foam fire extinguishing agents.

[0056] 6. This invention uses biomass recycling to treat sludge, saving a significant amount of valuable land resources compared to sanitary landfill, and turning waste into treasure to create greater value. Simultaneously, as a method for the harmless treatment of excess sludge, it alleviates the protein shortage problem for foam fire extinguishing agent manufacturers on a macro level, and enables them to obtain considerable recycling and treatment fees on a micro level, thus reducing production costs. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of the structure of EPS-ALE flame retardant particles, where 1 is nano-silica, 2 is an alginate hydrogel layer, and 3 is an extracellular polymer layer. Detailed Implementation

[0058] The present invention will now be described in further detail with reference to the embodiments.

[0059] In the following embodiments, the residual sludge used is return sludge from a municipal wastewater treatment plant, and the specific parameters are as follows: SV 30 =36,MLSS=5740,MLVSS=2540,SVI 30 =62.7178.

[0060] Example 1: Screening of extracellular polymer extraction methods

[0061] Take 100ml of the remaining sludge, centrifuge at 4℃ and 4000r / min for 20min, discard the supernatant and collect the wet sludge at the bottom;

[0062] Ultrasonic method: Take 3g of wet sludge, put it into a centrifuge tube and add distilled water to 50ml. Ultrasonicate at 20kHz and 40W for 3min in an ice-water bath. Then centrifuge at 4℃ and 4000r / min for 20min. Keep the supernatant and filter the supernatant through a 0.45μm filter membrane to obtain an extracellular polymer solution.

[0063] H2SO4 method: Take 3g of wet sludge and put it into a 250ml Erlenmeyer flask. Add distilled water to 50ml and add 1mol / L H2SO4 to adjust the pH to 2. Heat the Erlenmeyer flask in a water bath at 400r / min and 80℃ for 35min. During this process, cover the mouth of the Erlenmeyer flask with aluminum foil to prevent evaporation. Then, put the mixture into a centrifuge tube and centrifuge at 4℃ and 4000r / min for 20min. Keep the supernatant and filter the supernatant through a 0.45μm filter membrane to obtain an extracellular polymer solution.

[0064] Na2CO3 method: Take 3g of wet sludge and put it into a 250ml conical flask. Add distilled water to 50ml and add 1mol / L Na2CO3 solution to adjust the pH to 11. Heat the conical flask in a water bath at 400r / min and 80℃ for 35min. During this process, cover the mouth of the conical flask with aluminum foil to prevent evaporation. Then, put the mixture into a centrifuge tube and centrifuge at 4℃ and 4000r / min for 20min. Keep the supernatant and filter the supernatant through a 0.45μm filter membrane to obtain an extracellular polymer solution.

[0065] Extracellular polymers (ECPs) are mixtures composed of proteins, polysaccharides, and DNA. The content of ECPs obtained using different methods was characterized by expressing the content of proteins, polysaccharides, and DNA. Bovine serum albumin (BSA) was used as a standard, and the protein content in the samples was determined using a rapid protein assay kit. A glucose standard curve was used, and the polysaccharide content in the samples was determined using the anthrone-sulfuric acid method. The DNA content was determined using the diphenylamine method with DNA standards as the standard. The extracted ECP yield = protein extraction yield + polysaccharide extraction yield + DNA extraction yield.

[0066] The extracted three extracellular polymer solutions were prepared into an aqueous solution (3% w / v) and sprayed onto the surface of linen fabric. The solution was sprayed three times (300 ml in total) on linen fabric of the same size (20×40 cm) and air-dried for 72 h.

[0067] Vertical burning tests were conducted in accordance with the "Vertical Method for Testing Burning Performance of Textiles (GB / T 5455-1997)" to determine the burn resistance of extracellular polymers using different extraction methods.

[0068] The experimental results are shown in Table 1 below:

[0069]

[0070] As can be seen from the results in Table 1 above, the extracellular polymer solution obtained by the Na2CO3 method has the best extraction yield and anti-burn properties.

[0071] Example 2 Screening of foam protein extraction methods

[0072] Take 100ml of the remaining sludge, centrifuge at 4℃ and 4000r / min for 20min, discard the supernatant and collect the wet sludge at the bottom;

[0073] Ultrasonic method: Take 3g of wet sludge, put it into a centrifuge tube and add distilled water to 50ml. Ultrasonicate in an ice-water bath at 80kHz and 80w power for 40min. Then centrifuge at 4℃ and 4000r / min for 30min. Keep the supernatant, which is the foam protein stock solution.

[0074] NaOH method: Take 3g of wet sludge, put it into a 100ml pressure bottle, add distilled water to 50ml, add 1mol / L NaOH solution to pH=12, heat in an oil bath at 100r / min and 120℃ for 4h, after the pressure bottle cools to room temperature, centrifuge at 4℃ and 4000r / min for 20min, retain the supernatant, which is the foam protein stock solution.

[0075] Bioenzymatic method: Take 3g of wet sludge and put it into a 250ml conical flask. Add distilled water to 50ml, add 1mol / L NaOH solution to pH=10, and then add alkaline protease with a concentration of 6500U / g (wet sludge). Heat the conical flask in a water bath at 100r / min and 55℃ for 4h. During this process, cover the mouth of the conical flask with aluminum foil to prevent evaporation. Then, put the above mixture into a centrifuge tube and centrifuge at 4℃ and 4000r / min for 20min. Keep the supernatant, which is the foam protein stock solution.

[0076] Ozone micro-aeration method:

[0077] 1. Cultivate the excess sludge. The excess sludge is cultivated at 20±3℃ to obtain a sludge suspension. The cultivation method adopts the SBR process, with an effective reactor volume of 10 L and an operating cycle of 6 hours. Intermittent influent and effluent operation is used. Aeration is achieved through microporous sand aerators, with a timer controlling the aeration time and a gas flow meter adjusting the aeration rate within the reactor. The pH value of the reactor is controlled at 6-8, and the dissolved oxygen is controlled at 2-6 mg / L.

[0078] 2. Take 50 ml of sludge suspension and put it into a 250 ml flask. Immerse the flask in a 40 kHz ultrasonic bath with an ultrasonic intensity of 0.32 W / mL of sludge suspension. Cool it with 3.5℃ cold water.

[0079] 3. After ultrasonic treatment for 10 minutes, ozone is introduced into the flask in a micro-aeration manner, with an ozone concentration of 9 mgO3 / L.

[0080] The speed was 0.3 L / min, the contact time was 10 min, and ultrasonic treatment continued during the contact process.

[0081] 4. Place the treated suspension into a centrifuge and centrifuge at 4000 rpm and 20℃ for 15 minutes.

[0082] 5. Take the precipitate (biomass) after centrifugation and add it to the protein extraction mother liquor at a volume ratio of 1:10. Stir and extract at 40℃ for 15 minutes to obtain the maximum protein solubility. The protein extraction mother liquor used is a NaOH aqueous solution with pH=11.

[0083] 6. Place the mixture from step 5 into a centrifuge and centrifuge at 3000 rpm and 20°C for 15 minutes to obtain the supernatant, which is the foam protein stock solution.

[0084] The foam protein stock solutions obtained by the above four methods were dialyzed in 3500 Da dialysis bags for 24 hours, with the dialysis water changed every 12 hours to improve the dialysis effect. Samples from the bags were then placed in an oven and dried at 105℃ for 2 hours to obtain protein powder. The protein extraction rate was determined using the Kjeldahl method.

[0085] The protein powders obtained by the different methods described above were each prepared into 1 wt% protein solutions using a 0.2 mol / L phosphate solution at pH=7. 30 mL of each protein solution was placed in a 100 mL beaker and homogenized at 5000 rpm for 2 min. The homogenate was immediately transferred to a graduated cylinder, and the foam volumes V1 and V2 were recorded after homogenization stopped and 30 min later. The formulas for calculating foaming ability (FAI) and foam stability (FSI) are as follows:

[0086]

[0087] In the formula, V1 is the foam volume when homogenization stops; V2 is the foam volume 30 min after homogenization stops.

[0088] The experimental results are shown in Table 2 below:

[0089]

[0090] The results in the table above show that the NaOH method and the ozone micro-aeration method have good protein extraction rates and foaming properties, with the ozone micro-aeration method being the optimal one.

[0091] Example 3: Preparation of Fire Extinguishing Agent

[0092] A multiphase intumescent foam fire extinguishing agent based on residual sludge comprises separately packaged gas and liquid-solid phases. The gas phase is a driving gas, contained in a driving gas canister; the liquid-solid phase is a mixture of foam protein stock solution and EPS-ALE flame-retardant particles at a mass ratio of 1:0.15, contained in a liquid-solid phase storage tank. The preparation method of the fire extinguishing agent is as follows:

[0093] 1. Take the remaining sludge, centrifuge at 4℃ and 4000r / min for 20min, discard the supernatant and collect the wet sludge at the bottom;

[0094] 2. Take 3g of wet sludge and place it in a 250ml Erlenmeyer flask. Add distilled water to a final volume of 50ml. Add 1mol / L Na2CO3 solution to adjust the pH to 11. Heat the Erlenmeyer flask in a water bath at 400r / min and 80℃ for 35min, covering the mouth of the flask with aluminum foil during this process to prevent evaporation. Then, transfer the mixture to a centrifuge tube and centrifuge at 4℃ and 4000r / min for 20min. Filter the supernatant through a 0.45μm filter membrane to obtain the extracellular polymer solution. Reserve the bottom precipitate after centrifugation. Repeat step 2 to obtain the required amount of extracellular polymer solution and precipitate.

[0095] 3. Take the extracellular polymeric solution from step 2 and dialyze it in a 3500 Da dialysis bag for 24 hours, changing the dialysate every 12 hours. Transfer the dialysate extract to a 250 ml glass beaker. At room temperature, slowly stir the dialysate extract at 100 rpm, continuously monitoring the pH change with a pH electrode. While stirring, add 1 M hydrochloric acid (HCl) to the dialysate extract to adjust the pH to 2.2 ± 0.05. Then transfer the dialysate extract to a 50 ml centrifuge tube and centrifuge at 4000 rpm and 4°C for 20 minutes. Collect the gel-like particles at the bottom, which are acidic ALE. Slowly add 0.1 mol / L Na2CO3 solution to the gel-like particles while slowly mixing them with a glass rod until the pH reaches 8.5, obtaining an alginate solution.

[0096] 4. The obtained alginate solution was freeze-dried under vacuum at -70℃ for 72 hours to obtain dried alginate. The dried alginate was then mixed with a Na2CO3 solution with a pH of 8.3-8.7 to prepare a 3% (mass ratio) alginate compound solution.

[0097] 5. Completely immerse nano-silica with a particle size range of 70-200nm into the above excess alginate compound solution. After soaking for 24h, add 0.1M CaCl2 solution to the alginate compound solution at a rotation speed of 80r / min until gel particles are observed to be generated in the solution. Vacuum freeze-dry at -70℃ for 72h, collect the gel particles, and obtain nano-silica coated with an alginate hydrogel layer.

[0098] 6. Dilute the extracellular polymer solution obtained in step 2 with water, then add dicyandiamine to prepare a flame retardant solution with an extracellular polymer solution content of 20 wt% and a dicyandiamine content of 5 wt%. Completely immerse the nano-silica coated with an alginate hydrogel layer into the flame retardant solution and heat at 60 r / min and 40℃ for 25 min. Then remove the resulting gel particles and freeze-dry them under vacuum at -70℃ for 72 h to obtain EPS-ALE flame retardant particles.

[0099] 7. Take 3g of the bottom precipitate obtained from centrifugation in step 2, place it in a 100ml pressure bottle, add distilled water to 50ml, add 1mol / L NaOH solution to pH=12, heat in an oil bath at 100r / min and 120℃ for 4h. After the pressure bottle cools to room temperature, centrifuge at 4℃ and 4000r / min for 20min. Take the supernatant and dialyze it in a 3500Da dialysis bag for 24h, changing the dialysis water every 12 hours to improve the dialysis effect. After dialysis, take the sample from the bag and dry it in an oven at 105℃ for 2h to obtain protein powder. Prepare a 3wt% solution of the protein powder with 0.2mol / L phosphate solution at pH=7 to obtain foam protein stock solution.

[0100] 8. Mix the foam protein stock solution with EPS-ALE flame retardant granules at a mass ratio of 1:0.15, stir in a mixer for 5 minutes, and then store in a liquid-solid phase storage tank.

[0101] 9. Nitrogen, argon, and heptafluoropropane in a molar ratio of 45:40:15 are used as driving gases and stored in a driving gas tank.

[0102] Example 4

[0103] A multiphase expandable foam fire extinguishing agent based on residual sludge was prepared according to the method in Example 3, except that the foam protein stock solution was prepared according to the following method:

[0104] 1. Take 3g of the bottom precipitate obtained from centrifugation in step 2, put it into a 100ml pressure bottle, add distilled water to 50ml, disperse evenly, and obtain sludge suspension.

[0105] 2. Take 50 ml of sludge suspension and put it into a 250 ml flask. Immerse the flask in a 40 kHz ultrasonic bath with an ultrasonic intensity of 0.32 W / mL of sludge suspension. Cool it with 3.5℃ cold water.

[0106] 3. After ultrasonic treatment for 10 minutes, ozone is introduced into the flask in the form of micro-aeration. The ozone concentration is 9 mgO3 / L, the flow rate is 0.3L / min, and the contact time is 10 minutes. Ultrasonic treatment continues during the contact process.

[0107] 4. Place the treated suspension into a centrifuge and centrifuge at 4000 rpm and 20℃ for 15 minutes.

[0108] 5. Take the precipitate (biomass) after centrifugation and add it to the protein extraction mother liquor at a volume ratio of 1:10. Stir and extract at 40℃ for 15 minutes to obtain the maximum protein solubility. The protein extraction mother liquor used is a NaOH aqueous solution with pH=11.

[0109] 6. Place the mixture from step 5 into a centrifuge and centrifuge at 3000 rpm and 20°C for 15 minutes to obtain the supernatant. Place the supernatant in an oven and dry it at 105°C for 2 hours to obtain protein powder. Prepare a 3wt% solution of the protein powder with a 0.2 mol / L phosphate solution with pH=7 to obtain the foam protein stock solution.

[0110] Example 5

[0111] A multiphase expandable foam fire extinguishing agent based on residual sludge was prepared according to the method of Example 3, except that the particle size range of the nano-silica used was 200-400 nm.

[0112] Comparative Example 1

[0113] A multiphase expandable foam fire extinguishing agent based on residual sludge was prepared according to the method in Example 3, with the following difference:

[0114] The preparation method of flame-retardant particles is as follows:

[0115] 1. Take the remaining sludge, centrifuge at 4℃ and 4000r / min for 20min, discard the supernatant and collect the wet sludge at the bottom;

[0116] 2. Take 3g of wet sludge and place it in a 250ml Erlenmeyer flask. Add distilled water to a final volume of 50ml. Add 1mol / L Na2CO3 solution to adjust the pH to 11. Heat the Erlenmeyer flask in a water bath at 400r / min and 80℃ for 35min, covering the mouth of the flask with aluminum foil during this process to prevent evaporation. Then, transfer the mixture to a centrifuge tube and centrifuge at 4℃ and 4000r / min for 20min. Filter the supernatant through a 0.45μm filter membrane to obtain the extracellular polymer solution. Reserve the bottom precipitate after centrifugation. Repeat step 2 to obtain the required amount of extracellular polymer solution and precipitate.

[0117] 3. Dilute the extracellular polymer solution obtained in step 2 with water, then add dicyandiamine to prepare a flame retardant solution with an extracellular polymer solution content of 20 wt% and a dicyandiamine content of 5 wt%. Completely immerse nano-silica particles with a particle size of 70-200 nm into the flame retardant solution, heat at 60 r / min and 40℃ for 25 min, then remove the resulting particles and freeze-dry them under vacuum at -70℃ for 72 h to obtain EPS flame retardant particles.

[0118] Comparative Example 2

[0119] A multiphase expandable foam fire extinguishing agent based on residual sludge was prepared according to the method in Example 3, with the following difference:

[0120] The flame-retardant particles are nano-silica coated with an alginate hydrogel layer obtained in step 4 of Example 3, and are denoted as ALE flame-retardant particles.

[0121] Comparative Example 3

[0122] A multiphase fire extinguishing agent, the preparation method of which is as follows:

[0123] 1. Prepare foam protein stock solution, extracellular polymer solution and alginate solution according to the method of Example 3. Mix foam protein stock solution, extracellular polymer solution, alginate solution and nano-silica particles with a particle size of 70-200nm in a mass ratio of 1:0.15:0.15:0.15, stir in a stirrer for 5 minutes, and store in a liquid-solid phase storage tank.

[0124] 2. Nitrogen, argon, and heptafluoropropane in a molar ratio of 45:40:15 are used as driving gases and stored in a driving gas tank.

[0125] Comparative Example 4

[0126] A multiphase expandable foam fire extinguishing agent based on residual sludge was prepared according to the method in Example 3, with the following difference:

[0127] The flame-retardant particles are untreated nano-silica with a particle size range of 70-200nm.

[0128] Verification Example

[0129] The liquid-solid phase storage tank and the driving gas tank are connected to the foam mixing chamber through delivery pipelines, and flow meters are installed on the delivery pipelines. Then, the foam mixing chamber is connected to a nozzle to form a fire extinguishing system.

[0130] The performance of the fire suppression system was tested, and the test methods for each performance aspect are as follows:

[0131] 1. Viscosity was tested using the method described in GB15308-2006.

[0132] 2. The precipitate was tested using the method described in GB15308-2006.

[0133] 3. The foaming ratio is tested using the method described in GB15308-2006.

[0134] 4. The method for testing extinguishing time is as follows: At the start of the experiment, water and diesel fuel are poured into the oil pan sequentially, with a water-to-diesel volume ratio of 3:1, maintaining a liquid level approximately 5mm above the top of the pan. The oil pan is made of stainless steel, measuring 60mm × 60mm × 15mm, with a stainless steel plate thickness of 6mm. After 2 minutes, once the fuel combustion has stabilized, the pressure gauge is opened, allowing the driving gas to flow from the driving gas tank. Different driving pressures are achieved by adjusting the pressure gauge, and different gas-liquid ratios are obtained by adjusting the gas-liquid flow meter. The controlled liquid-to-gas ratio of the extinguishing system is 2:1, the liquid flow rate is 55L / h, and the driving pressure is 0.6 MPa. The driving gas is mixed with protein foam in the mixing chamber. The mixed foam is sprayed onto the oil pan through a pipe. The distance between the nozzle and the oil pan is 2m. A thermocouple is placed 15cm above the oil pan to record the temperature change during the extinguishing experiment. The extinguishing time is determined using a digital camera and an infrared thermal imager. All experiments were conducted outdoors, with wind speeds below 1.5 m / s and ambient temperatures between 20 and 25°C.

[0135] 5. The fire resistance time was tested using the method described in GB15308-2006.

[0136] The experimental results are shown in Table 3 below.

[0137]

Claims

1. A multiphase expandable foam extinguishing agent based on residual sludge, characterized in that: The product comprises separately packaged gas and liquid-solid phases, wherein the gas phase is a driving gas, and the liquid-solid phase is a mixture of foam protein and EPS-ALE flame-retardant particles at a mass ratio of 1:0.12-0.20; the EPS-ALE flame-retardant particles are prepared by: (1) Take the remaining sludge, centrifuge it, and collect the wet sludge at the bottom; (2) Disperse the wet sludge with water, then add Na2CO3 solution to adjust the pH to 10.5-11.5, then heat it with stirring, centrifuge it after treatment, filter the supernatant to obtain an extracellular polymer solution; (3) Using the extracellular polymer solution from step (2) as raw material, place it in a 3500 Da dialysis bag for dialysis. Adjust the pH of the obtained dialysis extract to 2.15-2.25 with acid while stirring. Then centrifuge the dialysis extract after pH adjustment, collect the gel-like particles at the bottom, and add Na2CO3 solution to the gel-like particles while stirring until the pH reaches 8.3-8.7 to obtain an alginate solution. (4) The alginate solution was freeze-dried under vacuum to obtain dry alginate, and then it was prepared into a 2-4 wt% alginate compound solution with Na2CO3 solution at pH 8.3-8.

7. (5) Soak the nano-silica in the alginate compound solution, then add CaCl2 solution to the alginate compound solution under stirring until gel particles are produced, then freeze dry under vacuum, collect the gel particles, and obtain nano-silica coated with alginate. (6) Mix the extracellular polymer solution, dicyandiamine and water from step (2) to obtain a flame retardant solution. Place the nano-silica coated with alginate into the flame retardant solution and heat it under stirring. Then take out the resulting gel particles and freeze-dry them under vacuum to obtain EPS-ALE flame retardant particles.

2. The multiphase expandable foam fire extinguishing agent based on residual sludge according to claim 1, characterized in that: In step (2), the mass ratio of wet sludge to water is 1:15-20, and the concentration of Na2CO3 solution is 0.5-1.5mol / L; in step (2), the sludge is heated at 75-85℃ for 30-40min.

3. The multiphase expandable foam extinguishing agent based on residual sludge according to claim 1, characterized in that: In step (3), dialysis is performed for 24-26 hours, during which the water used for dialysis is changed every 12-13 hours; in step (3), acid is added at a speed of 80-120 rpm, wherein the acid is 1-2 mol / L hydrochloric acid and the concentration of Na2CO3 solution is 0.05-0.15 mol / L.

4. The multiphase expandable foam fire extinguishing agent based on residual sludge according to claim 1, characterized in that: In step (5), the particle size of nano-silica is 70-400 nm.

5. The multiphase expandable foam extinguishing agent based on residual sludge according to claim 1 or 4, characterized in that: In step (5), nano-silica is soaked in an alginate solution for 22-26 hours, and the concentration of CaCl2 solution is 0.05-0.15 mol / L; in steps (4) and (5), the temperature of vacuum freeze drying is -65 to -75℃.

6. The multiphase expandable foam fire extinguishing agent based on residual sludge according to claim 1, characterized in that: In step (6), the content of extracellular polymeric solution in the flame retardant solution is 18-25 wt%, and the content of dicyandiamine is 3-8 wt%.

7. The multiphase expandable foam extinguishing agent based on residual sludge according to claim 1 or 6, characterized in that: In step (6), heat treatment is carried out at 38-45℃ for 20-30 minutes.

8. The multiphase expandable foam fire extinguishing agent based on residual sludge according to claim 1, characterized in that: The foam protein is a foam protein stock solution recovered from residual sludge.

9. The multiphase expandable foam fire extinguishing agent based on residual sludge according to claim 8, characterized in that: The foam protein stock solution is obtained using either method A or method B as follows: Method A: (A1) Take the remaining sludge, centrifuge it, and collect the wet sludge at the bottom; (A2) Take wet sludge or the sludge precipitate remaining after extracting extracellular polymers, disperse it with water, then adjust the pH to 11-13 with NaOH solution, then stir and heat at 115-125℃ for 3-5 hours, then cool and centrifuge, dialyze the obtained supernatant and dry it to obtain protein powder, and prepare a 2-4wt% solution with phosphate solution, which is the foam protein stock solution; Method B: (B1) The sludge remaining after the extraction of extracellular polymers in step (2) is precipitated as raw material, and the raw material is dispersed in water to obtain sludge suspension; (B2) Add the sludge suspension to a container and first sonicate it in a cold water bath at 0-5℃ for 5-15 minutes. The ultrasonic power is 35-45kHz, and the ultrasonic intensity is 0.2-0.4W / mL of sludge suspension. Then, while sonicating, introduce ozone into the sludge suspension in the form of micro-aeration. The ozone bubbles in the sludge suspension should be less than or equal to 50μm, and the ozone concentration should be 8-10mg O. 3 / L, ozone flow rate is 0.3-0.6L / min, ozone introduction time is 5-10min; (B3) The sludge suspension after ozone treatment is centrifuged, and the resulting precipitate is added to a sodium hydroxide solution with a pH of 11-13 for protein extraction. (B4) Centrifuge the mixture from step (3) to obtain the supernatant, dry the supernatant to obtain protein powder, and prepare a 2-4 wt% solution of the protein powder with phosphate solution, which is the foam protein stock solution.

10. The multiphase expandable foam fire extinguishing agent based on residual sludge according to claim 1, characterized in that: The driving gas is at least one of nitrogen, argon, and heptafluoropropane.

11. The multiphase expandable foam extinguishing agent based on residual sludge according to claim 10, characterized in that: The driving gas is a mixture of nitrogen, argon and heptafluoropropane.

12. The multiphase expandable foam extinguishing agent based on residual sludge according to claim 11, characterized in that: The molar ratio of nitrogen, argon, and heptafluoropropane is 45:40:

15.

13. A method for preparing a multiphase expandable foam fire extinguishing agent based on residual sludge as described in claim 1, characterized in that... Includes the following steps: (1) Mix foam protein and EPS-ALE flame retardant granules at a mass ratio of 1:0.12-0.20, stir evenly, and then pack into cans for later use; (2) Pack the driving gas into a can for later use.

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